The present invention relates to a novel method for the preparation of an organopolysiloxane compound substituted by a higher alkoxy group. More particularly, the invention relates to an efficient method for the preparation of an organopolysiloxane compound having, in a molecule, at least one alkoxy group of at least 4 carbon atoms bonded to the silicon atom.
As is well known, organopolysiloxanes or so-called silicones have excellent properties including high chemical and physical stability as well as inherent inertness to the human body so that silicones or, in particular, silicone oils are widely used as an ingredient in a wide variety of toiletry and cosmetic preparations. For example, eaux de cologne, toiletry soaps, enamels for manicure and pedicure, lipsticks, lip creams, shampoos, hair rinses, eye shadows, eyeliners, mascaras, cheek rouges and the like are sometimes formulated with an organopolysiloxane such as a dimethyl polysiloxane oil, methyl phenyl polysiloxane oil, octamethyl cyclotetrasiloxane, decamethyl cyclopentasiloxane, methyl hydrogen polysiloxane oil and the like. Some of toiletry and cosmetic preparations are formulated with an organopolysiloxane having at least one alkoxy group bonded to the silicon atom in a molecule such as a dimethyl polysiloxane-methyl polyoxyethylene copolymer, dimethyl polysiloxane-methyl polyoxypropylene copolymer, dimethyl polysiloxane-methyl polyoxyethylenepropylene copolymer, dimethyl polysiloxane-methylcetyloxysiloxane copolymer, dimethyl polysiloxane-methylstearyloxysiloxane copolymer and the like.
The method for the preparation of the above mentioned alkoxy group-containing organopolysiloxane is well known in the art of silicones. For example, Japanese Patent Publication No. 48-19941 teaches a method in which an organohydrogenpolysiloxane is subjected to a dehydrogenation condensation reaction with a higher alcohol in the presence of a strong alkali as the catalyst such as an alkali metal hydroxide and alkali metal alkoxide. Although the alkoxy residue of the higher alcohol can be bonded to the silicon atoms by this reaction, the siloxane linkages in the starting organohydrogenpolysiloxane are subject to the attack of the strong alkali used as the catalyst to cause scission so that the alkoxy group-containing organopolysiloxane obtained as the product neccessarily has a greatly decreased degree of polymerization or number of the silicon atoms in a molecule of, for example, 10 or smaller. Accordingly, it is eagerly desired to obtain an organopolysiloxane having a sufficiently high degree of polymerization and containing higher alkoxy groups of, for example, at least 4 carbon atoms in order to impart toiletry and cosmetic preparations with certain advantageous properties obtained only by formulating such a silicone.
An alternative method for the preparation of an alkoxy-substituted organopolysiloxane is the dehydrogenation condensation reaction between an organohydrogenpolysiloxane and an alcohol in the presence of a platinum compound as the catalyst. This platinum-catalyzed dehydrogenation reaction, however, can proceed only when the alcohol is a lower aliphatic alcohol such as methyl and ethyl alcohols and the reaction can hardly proceed when the alcohol is a higher alcohol having, for example, 4 or more carbon atoms in a molecule. Thus, no efficient method is known in the prior art for the preparation of an alkoxy-substituted organopolysiloxane, especially, when the alkoxy group has a large number of carbon atoms.